Galaxy Formation through Filamentary Accretion at z = 6.1

Abstract

We present Atacama Large Millimeter/submillimeter Array observations of the dust continuum and [C ii ] 158 μ m line emission from the z  = 6.0695 Lyman-Break Galaxy (LBG) WMH5. These observations at 0.″3 spatial resolution show a compact (∼3 kpc) main galaxy in dust and [C ii ] emission, with a “tail” of emission extending to the east by about 5 kpc (in projection). The [C ii ] tail is comprised predominantly of two distinct sub-components in velocity, separated from the core by ∼100 and 250 km s −1 , with narrow intrinsic widths of about 80 km s −1 , which we call “sub-galaxies.” The sub-galaxies themselves are extended east–west by about 3 kpc in individual channel images. The [C ii ] tail joins smoothly into the main galaxy velocity field. The [C ii ] line to continuum ratios are comparable for the main and sub-galaxy positions, within a factor two. In addition, these ratios are comparable to LBGs. We conjecture that the WMH5 system represents the early formation of a galaxy through the accretion of smaller satellite galaxies, embedded in a smoother gas distribution, along a possibly filamentary structure. The results are consistent with current cosmological simulations of early galaxy formation and support the idea of very early enrichment with dust and heavy elements of the accreting material.